30. Mammalian development Flashcards
What is considered day 0?
Fertilisation
What happens at day 1?
First cleavage
What happens at day 2?
2 cell stage then 4 cell stage
What happens from days 3-4?
8 cell stage
What happens at day 4?
Compacted morula
What is formed at day 5?
Early blastocyte
What is formed at day 6-7?
Late stage blastocyte (hatching)
What happens at day 8-9?
Implantation of the blastocyte
Why is there no yolk in mammal eggs?
Because all the nutrients the embryo requires are provided by the mother
What does the first cleavage produce?
Produces blastomeres that are developmentally equivalent (holoblastic cleavage)
What directions are the first and second cleavage?
First cleavage is a vertical cleavage
Second cleavage is one vertical and one horizontal
Why do cells become smaller with each division?
For the restoration of the nuclear to cytoplasm ratio
What happens with the activation of the embryo genome?
- Destruction of pre-stored mRNA
- But pre-stored proteins may continue to function and regulate development for some time
What is cadherin?
A calcium dependent cell adhesion molecule
What does cadherin do?
Mediates adhesion between blastomeres
- Cell outlines coalesce to form a morula
What does the cleavage of blastomeres result in?
Some cells enclosed within the inner compartment of the morula
What is cavitation?
What fluid begins to accumulate between blastomeres
What does cavitation result in the formation of?
A blastocoel
What is the outer layer of cells in the blastomeres?
The trophoblast/trophectoderm
What does the trophectoderm give rise to?
The placenta
What are the inner cells of the blastulation known as?
The inner cell mass
What does the inner cell mass give rise to?
The embryo
What is the purpose of the zona?
- The zona prevents cell-cell contact of the embryo and the oviduct wall so that there is no premature hatching
- Premature hatching causes a tubal pregnancy
What happens during zona hatching?
- Hatching occurs in the uterus just before implantation
- Blastocyst secretes proteases that weaken the zona so that it implants to the uterine epithelium